Word-formation structure exists exclusively in derivatives and compound words. It is important to distinguish between changes in word-formation structure at different stages of language development: The diachronic approach takes into account historical changes, while the synchronic approach studies the current state of the language. The differences between these approaches can be quite significant. The word-formation meaning and its formal indicator (derivative) form two sides of a single linguistic sign, i.e. derivateme, which is the signified and the signifier. Changes occur in language that affect morphemic structure and derivation. This includes such phenomena as etymologization, loss of morpheme productivity, haplology, folk etymology, and the law of analogy.